Marine ostracodes are useful in environmental studies because many species have geographical and bathymetrical distributions limited by water mass properties such as bottom water temperature, oxygen and salinity. In this study, we inspect the morphology of vestibulum which develop between duplicature and outer lamella on marginal carapace of ostracodes, and investigate the character of their shape for environmental factors. The samples were chosen from seas off the Japanese Islands and surrounding areas.Our main goals are 1) to determine the most useful ostracode species and genera indicating typical marine environments, 2) to determine the morphological characters of vestibulum shape corresponding to the marine environments, 3) to test the differentiation of vestibulum shape and structure changing by the environmental condition through culture experiment, 4) to apply the characteristics of vestibulum shape to the ostracode taxonomy and their phylogenetical analysis.These studies on the vestibulum were used to paleobiological analysis several ostracoda taxa, Aurila, Xestoleberis, Spinileberis, Vargula, Cytheropteron, Krithe, Ishizakiella etc.Through this research, a successful method for cultivating ostracodes was indeed found and in addition to being able to elucidate the life history of the species, it became possible to secure specimens for experiments. Further utilization of this technique may lead to the cultivation of other marine species.